1. Field of the Invention
The present invention relates to overhead cranes and in particular, to the suspended trolleys used thereon for the transport of a load along the horizontal beam thereof.
2. Prior Art
The present invention relates to both bridge cranes and boom cranes having a horizontal member along which a trolley travels to transport a load. Generally, there are two arrangements or methods for mounting a trolley, one by mounting the trolley on top of the horizontal member or beam and the second of suspending the trolley on wheels or rollers from the horizontal member.
The present invention relates to the latter arrangement. The horizontal member or boom is usually an "I" beam. The trolley is mounted on the lower cross member of beam by wheels which are mounted on the upper surface of the lower cross member or "I" flange. Usually the trolley has four wheels mounted to a frame and various load suspending and lifting means may be mounted to the frame, generally between the wheels or between two such trolleys running on parallel tracks ("I" beams).
The trolley is moved along the beam by a traction drive wheel which is biased against the lower side of the cross member of the beam on which the wheels ride. The prior method of biasing the drive wheel against the beam has employed various arrangements of springs. For example, U.S. Pat. Nos. 3,518,947 and 3,854,406 both show springs urging the wheel support upward. Another arrangement frequently seen in large over head bridge cranes having suspended trolleys is to mount the drive wheel on a lever between a pivot and a tension spring which biases the wheel upward against the I beam.
The spring biased arrangements have been found to cause relatively high wear and require frequent repair. This is particularly true in the spring biased lever arrangement noted above, where the drive wheels have at times worn out in about 24 hours of use. That particular arrangement also is somewhat difficult to service.
It is an advantage of the present invention that the rapid wear experienced with spring biased arrangements has been substantially eliminated and the useful life of the drive wheel extended far beyond that of the prior devices. It is a further advantage of the present invention that servicing and repair are simplified. A particular feature is the elimination of the spring, which is a part of the prior art arrangements. These and other advantages and features will become apparent from the following description and discussion of the invention and its embodiments.